The recent discovery of a ferroelectric response to a switching electric field in nematic phases exhibited by bent-core polar molecules, particularly 1,2,4-oxdiazole derivatives, could lead to new avenues for the development of electro-optic devices. For the first time, we report ferroelectric-like switching under the influence of a triangular wave electric field in the nematic phase exhibited by unsymmetrical achiral four-ring bent-core compounds. These bent-core molecules, exhibiting a large nematic phase range (>70 C), consist of two unequal lengths in two wings and possess a polar moiety at one end and an alkyloxy chain at the other end. An anomalous variation in spontaneous polarization as a function of temperature in the nematic phase is distinctly observed, which is similar to the results reported only in the low temperature region of the nematic phase. Electro-optical, current-response and dielectric studies of aligned samples corroborate earlier reports of the proposed polar structure of the cybotactic clusters and the ferroelectric-like polar switching of these nematic phases.

A block graph is a graph in which every block is a complete graph. Let G be a block graph and let A be the adjacency matrix of G. We first obtain a formula for the determinant of A over reals. It is shown that A is nonsingular over IF2 if and only if the removal of any vertex from G produces a graph with exactly one odd component.A formula for the inverse of A over IF2 is obtained, whenever it exists. We obtain some results for the adjacency matrices over IF2, of claw-free block graphs, which are the same as the line graphs of trees, and for the adjacency matrices of flowers, which are block graphs with only one cut-vertex.

Abstract-Blind adaptive multiuser detection for direct sequence code division multiple access (DS-CDMA) signals over static and time-varying intersymbol interference (ISI) limited channels is considered. Blind adaptive detectors must be robustified for ISI channels, when there is significant mismatch between the received signature vector and the transmitted code (assumed known at the receiver). A new low-complexity detector is presented that improves on some recently proposed methods without explicit estimation of the ISI channel. The key innovation is a reduced-rank detector architecture combined with an efficient subspace tracker that yields direct accurate estimation of the desired user's received signature. Several representative simulation examples of detector output signal-to-noise-and-interference ratio (SINR) for fading channels are provided in support of our claims of improved efficacy of the method.Index Terms-Blind adaptive filtering, code division multiple access (CDMA), multipath channels, multiuser detection.

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